In the cosmetic and pharmaceutical fields, many liquid products are sold in bottles. As soon as the bottle is opened for first-time use, contact with air inevitably entails oxidation which is detrimental to the product in the bottle. As a result, it is often impossible to go on using the product which has lost a part of its properties relatively quickly.
Other products are sold on some form of substrate, e.g. pads which have been pre-impregnated with toilet water or perfume. Once the packaging is broached, such substrates tend to dry out very quickly as well as providing a propitious medium for bacterial growth. The same disadvantages apply to make-up-removal wipes soaked in cleansing milk.
In consequence, using microcapsules was considered. Microcapsule technology is well known in the biomedical field. Microcapsules are spherical particles consisting of a solid envelope containing a liquid, solid or semi-solid principle.
Each microcapsule has diameter of between 50 μm and 1.5 mm and therefore actually constitutes a reservoir. The first industrial application for microcapsules was in the production of carbonless copy paper since which time this technology has been applied to resolve many problems in pharmacy. In practice, because their external covering inhibits exchange with the outside environment, microcapsules protect medicinal products from diverse chemical and physical phenomena such as humidity, heat and oxidation. Moreover, the rate at which active principles are released from microcapsules can be controlled and their bioavailability can be thus modulated. This can be achieved by varying a large number of different technical parameters, including the nature of the material used to produce the envelope, the relative proportions of the active principles, particle size, and the thickness of the envelope.
The above-mentioned properties have been exploited to produce a substrate acting as a medium for microcapsules, described for example in document FR-A-2.754.450. The material used is a foam such as a polyurethane foam, a polyethylene foam or any other polymer with a sponge-like consistency. The polyurethane foam, for example, is produced in a conventional process by condensation of a mixture of a polyol and isocyanate in the presence of water which leads to the release of carbon dioxide and therefore the formation of multiple cells which give the final polymer a sponge-like structure. The microcapsules are added to the above-mentioned three reagents and everything is thoroughly mixed together. When polymerization is complete, the resultant product is a sponge-like material with microcapsules distributed in the body of the foam which acts as a binder.
One of the characteristics of the material of the invention is that the cells communicate with one another so any products contained in the microcapsules can flow through the material when it is being used. It is important to include enough water in the reaction to induce the formation of open cells (i.e. inter-communicating cells). The ideal is of course to have a material in which 100% of the cells are open, but the above-mentioned applications are possible with a material in which only 60% of the cells are open. In practice, in addition to diffusion via the internal spaces of the cells, the products also diffuse as a result of impregnation of the material and capillary action. Application of a product contained in the microcapsules described in this document is achieved by exerting pressure on the substrate material in such a way as to burst the microcapsules to release the active principle(s) that they contain, so that these principles can reach the surface of the material by diffusion through the open cells.
However, using a substrate material such as is described in document FR-A-2.754.450 is associated with one major drawback. This is that the application surface can become contaminated with unwanted bodies such as dirt, dust or microorganisms, even if the material is sealed in packaging materials up till use. As a result, the active principles can become contaminated when they are released at the surface of the material so that topical application can lead to contamination of the skin and pathological consequences.